Recent studies have suggested that the sympathetic nervous system may play a role in the pathophysiology of human essential hypertension. A possible new approach to the determination of the level of sympathetic nervous system function in man involves the determination of circulating levels of the enzyme dopamine-beta-hydroxylase (DBH). This catecholamine biosynthetic enzyme is localized to catecholamine-containing vesicles in the adrenal medulla and in sympathetic nerves, is released with catecholamines in response to stimulation of these structures and is found circulating in the blood. The role of genetic factors in the regulation of serum DBH activity in man will be studied by population surveys, family studies, and biochemical investigation of the mechanisms by which these genetic factors are expressed. In addition, the effect of physiologic stimuli including the cold-pressor test and sodium depletion on sympathetic nervous system function as measured by serum DBH activity and catecholamine levels will be determined in control subjects and in patients with essential hypertension. These results will be correlated with biochemical measures of the function of the renin-angiotensin-aldosterone system and with levels of circulating prostaglandins. The results of these studies will increase our understanding of the meaning of measurements of DBH activity in man and will give further insight into a possible role of the sympathetic nervous system in essential hypertension and into the inter-relationship between the function of this portion of the nervous system and other vasoregulatory systems. BIBLIOGRAPHIC REFERENCES: Dunnette, J. and Weinshilboum, R.: Human Serum dopamine-beta-hydroxylase: Correlation of enzymatic activity with immunoreactive protein in genetically defined samples. Amer. J. Human Genet. 28:155-166, 1976. Weinshilboum, R. M., Dunnette, J. H., Raymond, F.A. and Schrott, H. G.: Genetic control of human serum dopamine-beta-hydroxylase. In: "Catecholamines and Stress" Ed. E. Usdin, R. Kvetnansky, and I. J. Kopin. Pergamon Press. 1976, pp. 293-303.